The principle of cleaning the conduits of a heat exchanger by a multiplicity of continuously recirculating rubber balls or the like is described in U.S. Pat. No. 2,801,824. Briefly, the ball-recirculating system includes a funnel-shaped extractor with sieve-like walls inserted in a descending exit duct for the carrier liquid (e.g. cooling water) to intercept the oncoming balls and guide them via a return or bypass connection to an entrance duct serving for the admission of fresh liquid. The outflowing liquid escapes through the interstices of the funnel. The impurities detached by the cleaning bodies from the inner tube walls of the heat exchanger as well as other contaminants (e.g. algae) entrained by the carrier liquid tend to accumulate in these interstices so that the sieve members of the extractor must be periodically cleansed. For this purpose, as likewise suggested in the aforementioned U.S. patent, the funnel may be split into two halves swingable about a common pivotal axis into a wide-open position in which parts of these halves are substantially parallel to the direction of flow.
A further development of this concept, described in U.S. Pat. No. 3,269,543, comprises a sieve box of narrow horizontal cross-section disposed beneath the funnel and provided at its lower end with a throttle valve which can be closed to force the accumulating liquid above that valve through the interstices of the box walls for cleansing same.